Railway signaling



7 Fl H. NICHOLSON RAILWAY SIGNALING Original Filed Apri 2 Patented Dec. 23, 1924.

STATES FRAN K H.1IICI-IOLSON, 0F WILKINSBURG, PENNSYLVANIA, ASSIGNO'R TO THE UNION SWITCH & SIGNAL COMPANY, OF SWISSVALE, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

RAILWAY SIGNALING.

Application filed April 21, 1921, Serial No. 463,234. Renewed January 22, 1923.

To all 107mm it may concern:

Be it known that I, FRANK I-I. NICHOL- soN, a citizen of the United States, residing at ilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented certain new and useful Improvements in Railway Signaling, of which the following is a specification.

My invention relates to railway signaling, and is particularly adapted to signaling of the type wherein roadside signals are con trolled in accordance with the presence and absence of trains through the medium of track circuits.

I will describe two forms of signaling ap paratus embodying my invention, and will then point out the novel features thereof in claims.

In the accompanying drawings, Fig. 1 is a diagrammatic view showing one form of signaling apparatus embodying my invention and having no moving parts between the track circuit and the signaling devices. Fig. 2 is a diagrammatic view showing an other form of signaling system embodying my invention wherein the signals are controlled by direct current relays which in turn are supplied with energy from alternating current track circuits.

Similar reference characters refer to similar parts in both of the views.

Referring first to Fig. 1, the reference characters E and E designate the track rails of a railway over which traflic normally moves in the direction indicated by the arrow. These rails are divided into track sections, of which only one section A-B is shown in the drawing. It is understood, however, that this section, together with the signaling apparatus associated therewith, would usually be duplicated in practice to form a complete signaling system embodying my invention. As here shown, the segregation of the track sections is accomplished by insulated joints 2, but I do not desire to be limited to this particular expedient.

The track section AB is provided with a track circuit including a transformer T, the secondary of which is connected across track rails adjacent the exit end of the section. The primary of this transformer is connected with a transmission line 3 which is constantly supplied with alternating signaling current from a generator 4. The track circuit also includes the primary of a transformer H which is connected across the rails adjacent the entrance end of the section and the purpose of which will be eX plained hereinafter.

Located adjacent the entrance end of the section AB is a signal S, adapted to indicate stop and proceed. As here shown, this signal comprises two lamps R and G, which, when illuminated, indicate stop and proceed, respectively.

Located adjacent the signal S are two electron tubes D and D each of which includes a heated filament 5, a grid 6, and a plate 7 Tube D is provided with a grid circuit which is energized by a secondary 10 on transformer I-I, whereas tube D is provided with agrid circuit which is energized from a secondary 11 on the transformer H. The right-hand terminal of secondary 10 is connected with the grid 6 of electron tube D, whereas the lefthand terminal of secondary 11 is connected with the grid 6 of tube D It follows, therefore, that when the grid 6 of tube D is positive with respect to the filament of this tube, the grid 6 of tube D is negative with respect to the filament of the tube D and vice versa.

The filament 5 of tube D is constantly heated by a secondary 8 of a transformer J through a circuit which will be obvious from the drawing. Filament 5 of tube D is like-' wise constantly heated from the secondary 9 on the same transformer. The primary 15 of transformer J is supplied with energy from the transmission line 3.

The electron tubes D and D are provided with a plate circuit which includes these two tubes in multiple, signal lamp G, and a source of alternating current, namely, the secondary 16 of transformer J. Since, as is well known, the plate-filament circuit of an electron tube is conductive in but one direction, the two tubes D and D? are connected in the circuit in opposite directions, so that consecutive half-waves of alternating current will flow through alternate tubes. This plate circuit passes from the left-hand terminal of secondary 16 of transformer J,

through wire 14, resistance 12, wire 13, lamp G, wire 17, thence, when the left-hand terminal of secondary 16 is positive, from plate to filament of. tube 1), thence over wires 18 and 1.9 to the right-hand terminal: of secondary 16. When the right-hand terminal of secondary 16 is positive the circu-it may be traced inthe opposite directionthrouglr wires 19- and 21-, plate tofilament 0]": tube D wires 20 and 17, lamp G, resistance 12, and wire 14 to the lefthand terminal of secondary 16. It follows, that in so far as this plate circuit is concerned,

when. the plate 7 0t tube D is positive, the

plate 7 oi. tube D is negative, with respect to the filaments 5..

The behavior'of the electron tubes D and D as influenced by the applied grid and plate potentials from transformers H and J ,v respectively, is as tollowsz. Considering,

tube D, it transformer is de-energ-ized', grid 6 will be at the same potential as the filament 5-, and hence produce no efiect.

Whenthe alternating potential from transformer. it applied to plate 7 is positive, electrons will be drawn from the filament to'the plate and current will flow in the plate circuit, The potential due to trans-former J is relatively low, so that but asmall current will flow due to thispotential alone, the im pedan'ce of; the tube will be high and the current will not be sufficient to illuminate lamp- Gr. l/Vhen' the potential due to transformer J is negative, electrons will be repolled from plate 'Z and the plate circuit of tube D will be non-conducting Elie alternating potential applied between the grid and filament from transformer H is relatively high. If this potential is positive when the potential due to J: is positive, that is, it the.- potentials of H. and J are in phase, the potential on the grid will neutralize the space charge of the electrons in the tube, greatly lowering the impedance ottheplate circuit and permitting a: larger current to how so as tofilluminate signal lamp- Gr. Iflhowever, transformer H- is reversed witli respectto J so that the potential on the grid is negative when that on; the plate ispositive, the platecu'rrent will be reduced to a. very low value or to zero; if the potential' on the gridispositive when that on the plate is negative, electrons willi' be re pelled from: the plate so that the plate current in this case is likewise low. In other words, when, and only when the grid: and

plate circuits are energized 111 such: a direction that the grid and plate voltages are simultaneously in the same direction, cur.- rent oi one-half wave from transformer secondary- 16 will: flow through lamp G and tubeD, whilecurrent of. the other half.- wave will flow through lamp Gr and tube D with the result that lamp will be illuminated. This is thecondition wheln track section:

AB is unoccupied, and under this condition it will be clear that signal S indicates proceed.

Stop signal lamp R is connected by wire 23 with the middle point 01 trans-former secondary 16, while the other terminal oi this lamp is connected through wire 22 with the plate circuit at a: point 42 between lamp G and resistance 12. Resistance 1-2 ismade equal to the impedance of the plate circuit including lamp G and tubes D and D when lamp- G is illnminated,-and so it will be seen that when normal current is flowing in the plate circuit and lamp G is illuminated the potential of the point 42' will be substantially equal to the potential at the middle point of transformer secondary 16. The result of this is that. at such times lamp R is extingu-ished.

I will now assume thata train enters the track section AB, thereby discontinuing the supply of track circuit energy to transformer H. The grid circuits of the electron tubes are then dc-energized so that the impedance ot the electrontubes D and l) is greatly increased,- and" the flow 0t current through lamp G is diminished so that lamp G is no longer illuminated Under this conditioir it is obvious that the potentials of point 42- and of the middle point of secondary 16 are no longer equal so that a flow of current then takes place through lamp it. This current is suflicient to illuminate lamp Rv so that signal S then indicates stop.

In. Fig- 1 I have shown no means "for providing what is known as the caution indication, that is, there is no means associated with signal S for indicating that the track section to the right of point B is occupied. This is torthe reasonthat such means forms no part of my invention in so far as the apparatus shown in Fig. 1 is concerned. Any suitable means, however, may be en'iployed for accomplishing this third indication when desired;

Referring. now to Fig; 2, the track rails E andE aredivided by insulated joints 2 into a. plurality of successive track sections AB, B C, etc., and each section is provided. with a roadside signal which is designated by the reference character S with an exponent corresponding to the location. As shown in Fig 2, each of these signals. is of the semaphore type, adapted: to indicate stop, caution or proceed according as the III? line 3, through a pole-changer operated by the adjacent signal, each of which polechangers is designated P with a suitable exponent. Each pole-changer is reversed during the movement of the signal between stop and caution positions, and so the section in the rear of an occupied section is supplied with alternating current of one relative polarity which I will term the reverse polarity, whereas all other sections are supplied with current of the opposite relative polarity, which I will term normal polarity.

Each track circuit also comprises a transformer designated H with a suitable eX- ponent, the primary of which is connected across the track rails at the entrance end of the section, and the secondary of which con trols the corresponding signal S through the medium of apparatus which I will now describe.

Each signal S is controlled directly by a relay deisgnated by the reference character F with a suitable exponent. Each of these relays is of the usual direct current type, having a neutral armature responsive to the presence and absence of current, and a po larized armature responsive to the direction of flow of current through the relay winding. The winding for this relay is in two sections, designated 27 and 27', which sec tions are connected at the middle so that the relay is what may be termed a differential polarized relay. That is, if current flows into the relay through wire 28 and passes through the upper section 27 the neutral armature will be closed and the polarized armature will be swung to one extreme position. If current enters the relay through wire 28, but flows through the lower section 27, the neutral armature will still be closed but the polarized armature will be swung to its opposite extreme position.

Referring particularly to location A, the signal S is provided with a caution indication circuit which passes from a secondary 29 of transformer J through wire 30, neutral contact 31 of relay F wire 32, operating mechanism of signal S, and wire 33 to secondary 29. The signal is also provided with a proceed indication circuit which passes from secondary 29, through wire 30, contact 31, wire 3 polarized contact 35, wire 36, operating mechanism of the signal and wire 33 to secondary 29. The caution indication circuit is, of course, closed when either winding of relay E is energized, but the proceed indication circuit is closed only when contact 35 is swung to the left, and this occurs only when the upper winding 27 is energized. The controlling circuits for each signal are the same as those for signal 8.

Still referring to the apparatus associated with signal S, the relay E is supplied with current from a secondary 16 of the transformer J and this supply is governed by two electron tubes D and D which in turn are controlled by the transformer H The electron tube filaments 5 are heated by a secondary 8 on a transformer J these filaments as here shown being connected in series, instead of in multiple as in Fig. 1. Tube D is provided with a grid circuit which passes from the right-hand terminal of secondary 23 of transformer H through wire 25, grid 6, filament 5, and wires 38 and 24 to the middle point of secondary 23. Similarly, the grid 6 of tube D is connected with the left-hand terminal of secondary 23 through a wire 26, while the filament 5 of this same tube is connected with the middle point of secondary 23 by wires 41, 24c and 24;. It will be seen from the J foregoing, that at any given instant the polarities of the grids 6 of the two tubes D and D are opposite; that is, when the grid of tube D is positive with respect to its associated filament, the grid of tube D is negative with respect to its associated filament.

The circuit of the secondary 16 of transformer J comprisestwo branches, one of which includes section 27 of the winding of relay F and electron tube D, whereas the other branch includes section 27 of the relay winding and electron tube D First considering tube D, the complete plate circuit for this tube is from the left-hand terminal of secondary 16, through wire 28, section 27 of the winding of relay F wire 37 tube D, and wires 38, 24 and 39 to right-= hand terminal of secondary 16. As for tube D the complete plate circuit'is from secondary 16, through wire 28, section 27 of the winding of relay F wire 40, tube D and wires 4L1 and 39 to secondary 16.

The primary 15 of transformer J is connected with the transmission line 3, and the parts of the apparatus are so adjusted that the plate circuit voltages in tubes D and D are either substantially in phase with or displaced substantially 180 from the grid voltages applied to these tubes by transformer H It follows that when polechanger P is in one position, the grid 6 of tube D will be positive with respect to the filament at the same instant that the plate 7 of this tube is also positive with respect to the filament. then this is the case, current will flow freely from secondary 16 through tube D and winding section 27 of relay F but substantially no current will flow through tube D and section 27, because the grid of this tube is negative with respect to the filament at theinstant that the plate 7 is positive with respect to the filament. Vhen pole-changer P is reversed, however, it will be obvious that current will flow through tube D but not through tube D, so that winding section 27 of relay F will be supplied with current but section 27 will be de-energized. It will be seen, therefore, that the relay F is energized only when track section A-B is unoccupied and that the polarized armature of relay F occupies one extreme position or the other according as pole-changer P is in normal or reverse position.

As shown in the drawing, track section C-D is occupied by a car or train WV, so that the supply of current to transformer H is discontinued. The potential in the plate circuit due to transformer J is relatively low, so that but a small current will flow through the relay windings when the grid circuit is Clo-energized, and this current magnetizes the relay in opposite direc tions in consecutive halI" cycles and hence will produce but a negligible effect, since this relay is, as previously stated, of the ordinary direct current type, and not readily operable upon alternating current. Signal S is, therefore, in the stop position, because substantially no rectified current is supplied to relay F by the adjacent transformer J Pole-changer P which is operated by signal S is in such position as to supply cur rent oi reverse relative polarity to the rails of section B-C. The result of this is that tube D at signal S is rendered conductive, so that winding section 27 of relay F is supplied with current. This causes energization of relay F in such direction that its polarized contact 35 is open, with the result that signal S indicates caution. The pole-changer P is therefore in such position that current or" normal relative polarity is supplied to the rails of section A-B, so that tube D for this section is rendered conductive. This causes winding section 27 of relay F to be energized, so that polarized contact 35 of this relay is closed, with the result that signal S is in the proceed position.

Although I have herein shown and described only two forms of signaling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a section of railway track, a source of current, a proceed signal for said section connected in circuit with said source in series with a resistance, a stop signal for said section connected with an intermediate point in said source and with the circuit vtor the proceed signal at a point between the latter signal and said resistance, and means controlled by the presence or absence o t trains in said section for varying the resistance of the connection between said source and the proceed signal.

2. In combination, a section of railway track, a source of current, a proceed signal for said section connected in circuit with said source in series with a resistance, a stop signal for said section connected with an intermediate point in said source and with the circuit for the proceed signal at a point between the latter signal and said resistance, a track circuit for said section, and means controlled by said track circuit for varying the resistance of the connection between said source and said proceed signal.

3. In combination, a section of railway track, a source of current, a proceed signal for said section connected in circuit with said source in series with a resistance, a stop signal for said section connected with an intermediatepoint in said source and with the circuit for the proceed signal at a point between the latter signal and said resistance, and means associated with said circuits for causing the currents flowing in said proceed signal and said resistance to be equal when said track section is unoccupied but not when it is occupied.

4. In combination, a section of railway track, a source of current, a proceed signal for said section connected in circuit with said source in series with a resistance, a stop signal "for said section connected with an intermediate point in said source and with the circuit for the proceed signal at a point between the latter signal and said resistance, a track circuit for said section, and means controlled by current from said track circuit. for causing equal currents to flow in said proceed signal and said resistance, and for unbalancing the currents in said elements when the supply of current from said track circuit ceases.

5. In combination, a section of railway track, a transformer the primary of which is connected with a source of alternating current, a proceed signal for said section connected in circuit with the secondary of said transformer in series with a resistance, a

stop signal for said section connected with an intermediate point on the secondary of said transformer and with the circuit for the proceed signal at a point between the latter signal and said resistance, and means associated. with the circuits of said signals for balancing the currents in said proceed signal and said resistance when said track section is unoccupied but not when it is occupied.

G. In combination, a section of railway track, a track circuit for said section including a source of alternating current; an electron tube having a filament, a grid and a plate; a plate circuit for said tube including a source of alternating current, a grid circuit for said tube supplied with current from said track circuit, and a signal for said sec-- tion controlled by said plate circuit,

til

7. In combination, a section of railway track provided with an alternating current track circuit, a signal and an electron tube for said section, a grid circuit for said electron tube energized by said track circuit, a plate circuit for said tube including a source of alternating current, and means associated with said plate circuit for controlling said signal.

8. In combination, a section of railway track provided with an alternating current track circuit, an electron tube having a heated filament, a grid and a plate, a grid circuit for said tube energized by said track circuit, a plate circuit for said tube including a source of alternating current, and a signal for said section controlled by said plate circuit.

9. In combination, a section of railway track provided with an alternating current track circuit; an electron tube having a heated filament, a grid and a plate; a grid circuit for said. tube energized from said track circuit, a plate circuit for said tube including a source of alternating current, said circuits being so arranged that the grid is positive with respect to the filament when the plate is positive with respect to the filament, and a signal for said section controlled by said plate circuit.

10. In combination, a section of railway track provided with an alternating current track circuit; two electron tubes each having a heated filament, a grid and a plate; a grid circuit for each tube energized from said track circuit in such manner that when the grid of either tube is positive with respect to its filament the grid of the other tube is negative with respect to its filament, a plate circuit including said two tubes in multiple and including a source of alternating current which is substantially in phase with the current in said track circuit, and a signal for said section governed by said plate circuit.

11. In combination, a section of railway track provided with an alternating current track circuit, a proceed signal and a stop signal for said section; two electron tubes each having a heated filament, a grid and a plate; a grid circuit for each tube energized from said track circuit in such manner that when the grid of either tube is positive with respect to its filament the grid of the other tube is negative with respect to its filament, a transformer the primary of which is supplied with alternating current in phase with the track circuit current, a plate circuit connected across the terminals of the secondary of said transformer and including said two tubes in multiple together with said proceed signal and a resistance in series, and a branch circuit including said stop signal and connected from an intermediate point on the secondary of said transformer to a point in said plate circuit between said proceed signal and said resistance.

12. In combination, a section of railway track, a source of current, a proceed signal for said section connected in circuit with said source in series with a resistance, a stop signal for said section connected with an intermediate point in said source and with a point in the circuit for the proceed signal, and means controlled by the presence or absence of trains in said section for varying the resistance of the circuit for said proceed signal, the parts being so proportioned and adjusted that the two points with which the stop signal. is connected are at the same potential when the section is unoccupied but not when it is occupied.

13. In combination, a section of railway track, a proceed signal for said section pro vided with a circuit including a source of current, means responsive to the presence and absence of trains in said section for modifying the resistance of said circuit, and a stop signal for said section connected with two points in said proceed signal circuit which are at the same potential when said section is not occupied by a train but which are not at the same potential when the section is occupied by a train.

14. In combination, a section of railway track, a signal circuit for said section including a source of current, means controlled by the presence and absence of trains in said section for modifying the resistance of said circuit, a branch for said circuit connected with two points in the circuit which are at the same potential when the section is unoccupied but at different potentials when the section is occupied, and signaling means for said section controlled by said signal circuit and by said branch.

15. In combination, a section of railway track, a signal circuit for said section including a source of current, means controlled by the presence and absence of trains in said section for modifying'g the resistance of said Circuit, a branch for said circuit connected with two points in the circuit which are at the same potential when the section is unoccupied but at different potentials when the section is occupied, and signaling means for said section controlled by said signal circuit and by said branch and arranged toindicate proceed when said two points are at the same potential and stop when said points are at different potentials.

16. In combination, a section of railway track, a signal circuit for said section including a source of current, means controlled by the presence and absence of trains in said section for modifying the reistance of said circuit, a branch for said circuit connected with an intermediate point in said source of current and with a point in said signal circuit, and signaling means for said section controlled by said signal circuit :and by said branch.

17. In combination, a .section of railway track, :a signal circuit for said section including .a source of current, rneans control-lo d by the presence and absence of trains said section for modifying the resistance of said circuit, :a branch for said circuit connected with :an intermediate point in said source of current aind'with a point in said signal cirwit, and signaling means for said section including .a proceed indication device controlled by said signal circuit :and a stop in dication zde ice controlled by said branch.

18. In combination, a section of .nailway track, .a signal circuit for said section including a source of current, means controlled by the presence and absence of trains in said section for modifying the resistance :of said circuit, a branch for said circuit connected with an intermediate point in said source of current and with a point in the circuit which is at the same potential as the first point when the section is unoccupied but not when the section is occupied, and signaling means for said section controlled by :saidsignal err cult .and by said branch.

19.. In combination, a section of railway track, a signal circuit for said section including asonrce of current, means controlled the presence-and absence of trains in said section for modifying "the reista-nce of said circuit, .a branch for said circuit connected with-anintermediate point in said source of current and with a .point in the .circnit which is at 'thesame potential as the firstpoint when the section is nnoccu'pied but not when the section is occupied, and signaling means for said section including :a'proceed indicaition device controlled :by said signal circuitand a stop indication device controlled by said branch.

'20. in combination, a section of railway track, a signal circuit for said section including a first signa linlg means and .a source of current, means controlled by the presence and absence of trains in said section for modifying the resistance :of said circuit, a branch around portion of said circuit, and :a second signaling means for said section controlled by said .circuietand by said branch.

21. In combination, a section of railway track, a signal circuit for said section including a source of current, means controlled by the presence and absence-of trains in said section for modifying the resistance 'o l said circuit, a branch around aportion of said circuit, and signaling mean-s tor said section including a proceed indication device controlled by said signal circuit and a stop indication device controlled by said branch.

22. In combination, a section of railway track, a signal circuit for said section including a sourceofcurrent, means controlled by the Presence and absence-of trains in said sect on [modifying an electrical characteristic of said circuit, a branch for said circuit connected with two points in "the circuit which are :at the same potential when the section is nneccnpied but at dii" tizrl-s when the section is occupied, and sin} inaling means for said sect-ion controlled by said signal circuit and by said branch.

23. In combination, a section of railway traclr, a circuit for said section including a first signaling means and :a source of current, mean-s controlled :by the presence and absence of trains in said section for modifying an electrical characteristic of said circuit, a branch around a portion of said circuit, and .a second signaling means for said section controlled by said circuit and by said branch.

24. In combination, :aseotion 20ft railway track, a signal circuit for said section in cluding a source of current, means controlled by the presence and absence of trains in said section for modifying an electrical characteristic of said circuit, a branch for said circuit connected with an intermediate point in said source of current and with .a :point in the circuit which is at the same potential .as the first :point when the .section .is-unoccupied but not when the section is occupied, and signaling means for said section controlled by said signal circnit and by said branch.

25. In combination, a section of railway 1 rack, signal circuit for said section including a source of current, means controlled by the presence an'dabsence of trains in said section for modifying the resistance of said circuit, abranch for said circuit so connected with the circuit as to carry considerably more current when the resistance of the circuit is high than when the resistance of the circuit is low, and signab ing means for said section controlled by said circuit and by said branch.

26. In combination, a section of railway track, a signal circuit for said section including a sonrce vof current, means controlled by the presence :and absence of trains in said section for modifying the resistance of said circuit, a branch for said circuit so connected with the circuit as to carry considerably more current when the resistance of the circnit is high than when the resistance of the circuit is low, and signaling means for said section including .a proceed indication idevice controlled by said signal circuit .and .a stop indication device controlled by said branch.

27.. In combination, .a section of railway track, a signal circuit for said section including a sourceof current, means controlled by the presence and absence of trains in said section for modifying the resistance of said iC-lICLtlt, a branch for said circuit conneeted around the variable resistance inrent potenstrunientality in the circuit whereby the branch carries more current when the resistance of the circuit is high than when the resistance is low, and signaling means for said section controlled by said circuit and by said branch.

28. In combination, a section of railway track, a signal circuit for said section including a source of current, means controlled I by the presence and absence of trains in said section for modifying the resistance of said circuit, a branch for said circuit connected around the Variable resistance instrumentality in the circuit whereby the branch carries more current when the resistance of the circuit is high than when the resistance is low, and signaling means for said section including a proceed indication device controlled by said signal circuit and a stop indication device controlled by said branch.

29. In combination, a section of railway track, a signal circuit for said section including a source of current, train controlled means for causing the resistance of said circuit to be high when the section is occupied and low when the section is unoccupied, a branch for said circuit connected with two points which are at the same potential when the resistance of the circuit is.

low but at different potentials when the resistance is high, and signaling means for said section controlled by said circuit and by said branch.

30. In combination, a section of railway track, a signal circuit for said section including a source of current, train controlled means for causing the resistance of said circuit to be high when the section is occupied and low when the section is unoccupied, a branch for said circuit connected with two points which are at the same potential when the resistance of the circuit is low but at dii'l'erent potentials when the resistance is high, and signaling means for said section including a proceed indication device controlled by said signal circuit and a stop indication device controlled by said branch.

31. In combination, a section of railway track, a signal circuit for said section including a source of current, train controlled means for causing the resistance of said circuit to be high when the section is occupied and low when the section is unoccupied, a branch for said circuit connected with two points so chosen that the branch carries more current when the resistance of the circuit is high than when the resistance is low, and signaling means for said section controlled by said circuit and by said branch.

32. In combination, a section of railway track, a signal circuit for said section including a source of current, train controlled means for causing the resistance of said circuit to be high when the section is occupied and low when the section is unoccupied, a branch for said circuit connected with two points so chosen that the branch carries more current when the resistance of the circuit is high than when the resistance is low, and signaling means for said section including a proceed indication device controlled by said signal circuit and a stop indication device controlled by said branch.

33. In combination, a section of railway track, a signal circuit for said. section including a source of current, train controlled means for causing the resistance of said circuit to be high when the section is occupied and low when the section is unoccupied, a branch for said circuit connected with two points which are at the same potential when the resistance of the circuit is low but at different potentials when the resistance is high, one of said points being an intermediate point in said source, and signaling means for said section controlled by said circuit and by said branch.

84. In combination, a section of railway track, an electron tube, a plate circuit for said tube including a source of current, a grid circuit for said tube controlled by tratfie in said section, a branch for said plate circuit connected with an intermediate point in said source and with a second point in the circuit which has the same potential as the first point when said grid circuit is energized but not when it is deenergized, and signaling means for said section controlled by said plate circuit and by said branch.

35. In combination, a section of railway track, an electron tube, a plate circuit for said tube including a source of current, a grid circuit for said tube controlledby traflie in said section, a branch for said plate circuit connected with an intern'iediate point in said source and with a second point in the circuit which has the same potential as the first point when said grid circuit is energized but not when it is de-energized, and signaling means for said section including a. proceed indication device controlled by said plate circuit and a stop indication device controlled by said branch.

36. In combination, a section of railway track, an electron tube, a plate circuit for said tube including a source of current, a grid circuit for said tube controlled by traftie in said section, branch for said plate circuit connected with points so chosen that they have the same potential when the grid circuit is energized but different potentials when the grid circuit is de-energized, and signaling means for said section controlled by said plate circuit and by said branch.

37. In combination, a section of railway track, an electron tube, a plate circuit for said tube including a. source of current, a grid circuit for said tube controlled by trafiic in said section, a branch for said plate energized, and signaling means circuit connected with points so chosen that they have the same potential when the grid circuit is energized but different potentials when the grid circuit is tie-energized, and signaling means for said section including a proceed indication device controlled by said plate circuit and a stop indication device controlled by said branch.

38. In con'ib-ination, a section of railway track, an electron tube, a plate circuit for said tube including a source of current, a grid circuit for said tube controlled by traflie in said section, branch for said plate circuit connected with two points in the plate circuit which have the same potential when the grid circuit is energized but diii'crentpotentials when the grid circuit is defor said section controlled by said plate circuit and by said branch.

39. In combination, a section of railway track, an electron tube, a plate circuit for said tube including a source of current, a grid circuit for said tube controlled by traffic in said section, a branch for said plate circuit connected with two points in the plate circuit which have the same poten tial when the grid circuit is energized but different potentials when the grid circuit is tie-energized, and signaling means for said section including a proceed indication device controlled by said plate circuit and a stop indication device controlled by said branch.

40. In combination, a section of railway track, an electron tube, a plate circuit for said tube including a source of current, a grid circuit for said tube controlled by trai lie in said section, a branch for said plate circuit connected with two points in the plate circuit, and signaling means for said section controlled by said plate circuit and by said branch.

ll. In combination, a section of railway track, an electron tube, a plate circuit for said tube including a source ot current, a grid circuit for said tube controlled by traflie in said section, a branch for said plate circuit connected with two points in the plate circuit, and signaling means for said section including a proceed indication device controlled by said plate circuit and a stop indication device controlled by said branch.

d2. In conil'iiuation, a section of railway track, an electron tube, a plate circuit for said tube includingasource of cin'rent, a grid circuit for said tube controlled by tratlie in said section, a branch for said plate circuit connected with a intermediate point in said source and another point in the plate circuit, and signaling means for said section controlled by said plate circuit and by said branch.

43. In combination, a section oi railway track, an electron. tube, a plate circuit for said tube including a source of current, a grid circuit for said tube controlled by traili in said section, abranch for said plate circuit connected with said plate circuit in' such manner as to carry considerably more current when the grid circuit is de energized than when the grid circuitis energized, and signaling ineans tor said section controlled by said plate circuit and by said branch.

4:47. In combination, a section of railway track, an electron tube, a plate circuit for said tube including a source of current, a grid circuit for said tube controlled by traflie in said section whereby the resistance of said plate circuit is high when the section is occupied and low when the section is unoccupied, a branch for said plate circuit connected with two points which have the same potential when the resistance of the circuit is low but ditierent potentials when the resistance of the circuit is high, and signaling means for said section controlled by said plate circuit and by said branch.

e5. In combination, a section of railway track, an electron tube, a plate circuit for said tube including a source out current, a grid circuit for said tube controlled by traffic in said section whereby the resistance of said plate circuit is high when the section is occupied and low when the section is unoccupied, a branch for said plate circuit connected with two points which have the same potential when the resistance of the circuit is low but different potentials when the resistance of the circuit is high, one of said points being an intermediate point in said source of current, and signaling means for said section controlled by said circuit and by said branch.

e6. In combination, a section of railway track, a si 'na-l circuit including a source of current, means controlled by trarlic in said section and comprising an electron tube inchided in said circuit for varying the resistance of the circuit, a branch for said circuit connected with points having the same potential when the resistance ot'the circuit is low but different potentials when the resistance of circuit is high, and signaling means for said section controlled by said circuit and by said branch.

47. In combination, a section of railway track, a signal circuit including a source of current, nieans cont-rolled by trafl'ic in said section and comprising an electron tube included in said circuit for varying the resistance of the circuit, a branch for said circuit connected with points having the same potetnial when said section is not occupied but ditl'crent potentials when the section is occupied by a train, and signaling means for said section controlled by said circuit and by said branch.

48. In combination, a section of railway track, a signal circuit including a source of current, means controlled by traffic in said section and comprising an electron tube included in said circuit for varying the resistance of the circuit, a branch for said circuit connected with an intermediate point in said source of current and with a point in the circuit which has the same potential as the first point when the resistance of the circuit is low but not when the resistance of the circuit is high, and signaling means for said section controlled by said circuit and by said branch.

49. In combination, a section of railway track, a signal circuit including a source of current, means controlled by tratfic in said section and comprising an electron tube included in said circuit for varying the resistance of the circuit, a branch for said circuit connected with an intermediate point in said source of current and another point in said circuit, and signaling means for said section controlled by said circuit and by said branch.

50. In combination, a section of railway track, a signal circuit including a source of current, means controlled by traific in said section and comprising an electron tube included in said circuit for varying the resistance of the circuit, a branch for said circuit connected with the circuit in such manner as to carry considerably more current when the resistance of the circuit is high than when the resistance of the circuit is low, and signaling means for said section controlled by said circuit and by said branch.

51. In combination, a section of railway track, a signal circuit including a source of current, means controlled by trafiic in said section and comprising an electron tube included in said circuit tor varying the resistance of the circuit, a branch around a portion of said circuit, and signaling means for said section controlled by said circuit and by said branch. p

52. In combination, a section of railway track; a circuit including a source of current, a resistance, a proceed signal device and an electron tube; a grid circuit for said tube controlled by traffic in said section, a stop signal device connected with an intermediate point in said source of current and with a point in said circuit which is the same potential as the first-mentioned point when the section is unoccupied.

53. In combination, a section of railway track; a circuit including a source of current, a resistance, a proceed signal device, and an electron tube, a grid circuit for said tube controlled by traffic in said section, and a stop signal device connected with said circuit at a point between said resistance and said proceed signal device, and also connected with an intermediate point in said source of current.

54. In combination, a section otrailway track, a track circuit for said section includ ing a source of alternating current and the primary of a transformer having two secondaries, two electron tubes, grid circuits for said tubes supplied with potential from said two secondaries respectively, and signaling means for said section controlled by said a electron tubes.

55. In combination, a section of railway track, a track circuit for said section including a source of alternating current and the primary of a transformer having two secondaries, two electron tubes, grid circuits for said tubes supplied with potential from said two secondaries respectively, in such manner that when the grid in one tube is positive with respect to its filament the grid in the other tube is negative with respect to its filament, and signaling means for said section controlled by said electron tubes.

56. In combination, a section of railway track, two electron tubes, train controlled means for said section operating when the section is unoccupied to apply an alternating difference of potential to the grid and the filament of each tube, the grid of one tube being positive with respect to its filai, ment at the instant that the grid of the other tube is negative with respect to its filament, and signaling means fQlfSZtlCl sect1on controlled by said tubes.

57. In combination a section of railwa track, two electron tubes, train controlled means for said section operating when the section is unoccupied to apply an alternating difference of potentialto the grid and the filament of each tube,"the grid of one tube. being positive with'respect to its filament at the instant that the grid of the other tube is negative with respect to its filament, a plate circuit including said two tubes in multiple and a source of alternating current, said plate circuit being so arranged that the plate of each tube is positive with respect to its filament at the same instant the grid of the tube is positive with respect to its filament, and signaling means for said section controlled by said plate circuit.

58. In combination, a section of railway track, two electron tubes, train controlled means for said section operating when the section is unoccupied to apply an alternating differenceof potential to the grid and the filament of each tube, the grid of one tube being positive with respect to its filament at the instant that the grid of the other tube is negative with respect to its filament, means for applying an alternating current to the plate and filament of each tube in such manner that the plate is positive with respect to the filament at the same instant the grid is positive with respect to the filament, and signaling means for sa d section controlled by the currents flowing in the plate circuits of said tubes.

59'. In combination, a section of railway track, two electron tubes, train controlled means for said section operating when the section is unoccupied to apply an alternat ing difference of potential to the grid and the filament of each tube, the grid of one tube being positive with respect to its filament at the instant that the grid of the other tube is negative with respect to its filament, a plate circuit including said two tubes in multiple and a source of alternating current, said plate circuit being so arranged that the plate of each tube is positive with respect to its filament at the same instant the grid of the tube is positive with respect to its filament, and a signal lamp in cluded in said plate circuit.

60. In combination, a section of railway track, two electron tubes, train controlled means for said section operating when the section is unoccupied to apply an alternating difference of potential to the grid and the filament of each tube, the grid of one tube being positive with respect to its filament at the instant that the grid of the other tube is negative with respect to its filament, means for applying an alternating current to the plate and filament of each tube in such manner that the plate is positive with respect to the filament at the same instant the grid is positive with respect to the filament, and a signal for said section including a lamp energized by the currents flowing in the plate circuits of said tubes.

61. In combination, a section of railway track, two electron tubes, a plate circuit including said tubes in multiple and a source of alternating current, said tubes being reversely connected so that when the plate of one tube is positive with respect to its filament the plate of the other tube is negative with respect to its filament, train controlled means operating when said section is unoccupiedto apply a difference of potential to the grid and filament of one tube and the reverse difference of potential to the grid and filament of the other tube, and signaling means for said section controlled by the plate circuit for said tubes.

62'. In combination, a section of railway track, a track circuit for said section including a source of alternating current and the primary of a transformer having two secondaries, two electron. tubes, grid circuits for said tubes supplied with potential from said two secondaries respectively, an electron tube having agrid circuit supplied with potential from the secondary of said transfoii'n'ier, a plate circuit for said tube,

' and signaling means for said section controlled by said plate circuit.

63. In combination, a section of railway track, a transmission line carrying alternating signaling current, a transformer the primary of which is connected with said transmission line and the secondary of which is connected with the rails of said section, a second transformer having its primary connected with said rails, an electron tube provided with a grid circuit including a secondary of said second transformer, a third transformer having its primary connected with said transmission line, a plate circuit for said tube including a secondary of said third transformer, a filament heating circuit for said tube including another second ary of said third transformer, and signaling means for said section controlled by said plate circuit.

64. In combination, a section of railway track, a transmission line carrying alternating signaling current, a track circuit for said section supplied with alternating current from said transmission line, an electron tube, a grid circuit for said tube supplied with alternating current from said track circuit, a plate circuit for said tube supplied with alternating current from said transmission line, and signaling means for said section controlled by said plate circuit.

65. In combination, a section of railway track, a transmission line carrying alternating signaling current, a track circuit for said section supplied with alternating current from said transmission line, an electron tube, a grid circuit for said tube supplied with alternating current from said track circuit, a plate circuit for said tube supplied with alternating current from said transmission line, a filament heating circuit for said tube also supplied with alternating current from said transmission line, and signaling means for said section controlled by said plate circuit.

66. In combination, a section of railway track, a transmission line carrying alternating signaling current, a track circuit for said section supplied with alternating current from said transmission line, two electron tubes for said section, a grid circuitfor each tube supplied with alternating potential from said track circuit in such manner that the grid of one tube is positive with respect to its filament at the instant the grid of the other tube is negative with respect to its filament, a plate circuit for said tubes supplied with alternating current from said transmission line and including the two tubes in multiple, and signaling means for said section controlled by said plate circuit.

67. In combination, a section of railway track, a transmission line carrying alternating signaling current, a track circuit for said section supplied with alternating current from said transmission line, two elcctron tubes for said section, a grid circuit for each tube supplied with alternating potential from said track circuit in such manner that the grid of one tube is positive with respect to its filament at the instant the grid of the other tube is negative with respect to its filament, a plate circuit for said tubes supplied with alternating current from said transmission line and including the two tubes connected in multiple in such manner that the plate of each tube is positive with respect to its filament at the same instant that the grid of such tube is positive with respect to its filament, and signaling means for said section controlled by said plate circuit.

68. In combination, a section of railway track, a signal circuit including a source of current and the filament and plate 01": an electron tube, a grid circuit for said tube controlled by the presence and absence of trains in said section, a branch for said signal circuit connected with two points in the circuit such that the voltage which is applied to the branch varies according as said grid circuit is energized or Clo-energized, and signaling means for said section con trolled by said signal circuit and by said branch.

In testimony whereof I aiiix my signature.

FRANK H. NICHOLSON. 

